This proposal involves an investigation into the mechanisms and significance of site specific, rec-independent recombination in Staphylococcus aureus. Three different but related recombination systems will be studied: site specific integration of a plasmid into a prophage (and vice versa); site specific reversible inversion of a DNA segment carried by a transposon; and the transposition mechanism of a site specific, repressor-controlled transposon that appears to be functionally and structurally related to the prophage just mentioned. The precise location and DNA sequences of the recombination sites will be determined, the recombination mechanisms will be analyzed genetically and biochemically, and the biological role of the recombination processes will be investigated, with special reference to the controls that govern the frequencies of the recombinational events and to the significance of these events with respect to molecular evolution and their regulation of cellular processes.